1. Field of Invention
This invention relates generally to the treatment of non-toxic wastewater, including water-borne waste material from residential, commercial and other sources, and particularly to an improved system for activated sludge wastewater treatment.
Wastewater treated by conventional wastewater treatment systems contains soluble, partially soluble and insoluble material as well as contaminates. Materials in the wastewater may be decomposable, partially decomposable or not decomposable. Decomposable and partially decomposable materials are referred to as biodegradable; that is, the material may be biologically broken down, or stabilized by bacterial action. Wastewater treatment systems are designed to provide controlled decomposition of wastes to reduce pollution, health hazards and offensive odors.
Decomposable material is stabilized in wastewater treatment systems by bacteria, protozoa, and other microorganisms. Bacterial consumption of material, creating energy and reproducing bacterial cells, is the foundation of activated sludge wastewater treatment.
Conventional wastewater treatment systems may include pretreatment, primary treatment, secondary treatment, and advanced treatment.
Pretreatment includes screening, comminuting (mechanical cleaning of screens by shredding solids to a size which can pass through screen openings), degritting, and grease and scum removal.
Primary treatment includes removal of suspended solids from wastewater by clarification and skimming, typically involving a tank or channel, reducing flow velocity, settling of heavier solids and skimming of relatively light solids. Primary treatment may include anaerobic digestion processes, aerobic digestion processes, or a combination thereof. Primary treatment systems typically include sludge collection mechanisms, sludge suction devices, grit removal devices, and sludge dewatering devices to reduce the volume of sludge to be disposed.
Secondary treatment systems are typically aerobic systems including an aeration phase and a clarification phase. Secondary treatment systems typically include an aeration tank, an air distribution system, a clarifier, sludge collection mechanisms, and sludge removing devices.
Advanced treatment includes further removal of suspended and dissolved organic solids by means including filtration, removal of pathogens and chloroforms by oxidation, chlorination or heating, precipitation of minerals, adsorption or other methods.
In the activated sludge process of primary or secondary treatment, microorganisms are contained in an activated sludge and mixed with incoming wastewater; the wastewater providing food for the microorganisms. Such mixing is accomplished in an aeration tank or channel. In the aerobic activated sludge process, oxygen is intimately mixed with the activated sludge and the wastewater, the microorganisms converting suspended organic solids into energy, carbon dioxide, water, and additional microorganism cells. The aerobic activated sludge process therefore typically includes (i) mixing of wastewater, activated sludge, and oxygen in an aeration tank, (ii) converting suspended organic solids, (iii) settling of activated sludge in the clarifier, (iv) returning the activated sludge to the aeration tank for further treatment, (v) removing purified liquor from the clarifier, and (vi) removing and disposing of the final, inert sludge.
In the further process of advanced treatment, the purified liquor from the clarifier is typically filtered. The filtered liquor is refined through chlorination, oxidation, or heating.
Current technology is generally practiced in relatively large plants providing wastewater treatment for communities. Various attempts have been made to develop a practical treatment system for use in individual applications or applications for relatively small communities.
Relatively small plants have not been economical to construct due to the requirement that the plant be designed to handle the maximum volume of waste that may require treatment from time to time, which maximum volume substantially exceeds the normal volume of wastewater. This results in a requirement to construct plants having substantially higher capacity than is normally needed. This problem is reduced in plants serving relatively large communities due to diversity of wastewater treatment requirements.
Current technology used in the design of activated sludge wastewater treatment plants provides a high amount of process control. Conventional design of such plants, however, requires the use of a large number of mechanical subsystems including pumps, blowers, gears, chains, and associated mechanical elements. The large quantity of mechanical parts makes such conventional systems expensive to construct and maintain as well as difficult to operate.
2. Related Art
Wastewater systems that attempt to improve various aspects of wastewater treatment are known to the prior art. Valdespino U.S. Pat. No. 3,220,706 discloses a sewage treatment system comprising, in combination, an aeration unit including a generally circular tank, a tangentially disposed adjustably-sized sewage inlet located along the wall of the tank, an overflow discharge line, a circulating pump, vertically adjustable air inlet means requiring blowers or compressors in the middle of said tank spaced from the bottom of the tank, blowers and a liquid spray ring around the upper interior portion of the tank having downwardly-directed orifices. Sewage introduced into the tank through tangential inlets rotates. Compressed air from the air inlet induces movement in the sewage vertically at right angles to the sewage rotation, resulting in rolling, swirling flow and exposure of sewage with oxygen in the air. The Valdespino disclosure includes a sump, an aeration tank, a settling tank, a sludge digestion tank, and various valves, blowers, and pumps connecting the various tanks.
Drewery U.S. Pat. No. 5,667,670 discloses a wastewater system including a pretreatment tank for aeration and activated sludge treatment, a wastewater tank, a sand filter, a T-filter for filtering sand or silica particles, a filtered water retaining chamber, and associated valves piping and controls. The filtered water retaining chamber includes a bladder utilized for backwashing the sand filter.
O'Brien U.S. Pat. No. 5,207,905 discloses a baffle system for a media filter bed that is backwashed by a turbulent stream.
Farabaugh U.S. Pat. No. 4,065,391 discloses fluid distributors for providing uniform distribution of a fluid throughout a bed of granular material.
Kos U.S. Pat. No. 4,202,774 discloses a flow distributor including means for decreasing velocity of fluid streams in a fluid bed biological reactor.
J. H. Duff, et al., U.S. Pat. No. 3,260,366 discloses apparatus for cleaning a filter bed including means for entraining gas in raw liquid, a filter chamber, a chamber including a filter bed and a gas space above the filter bed, and a tank for filtered liquid mounted above the chamber containing the filter bed.
Berrie U.S. Pat. No. 4,720,347 discloses apparatus for continuously filtering a suspension involving a granular filtrating with the suspension flowing though the granular filtrating mass as a vertical ascending current.